AS

Size of Continents and Seafloor Spreading

Sea Level- Number and Size of Continents

  • Pangaea: “supercontinent” that existed 260-240 million years ago
  • supercontinents have less coastlines, more harsh continental interiors
    • supercontinents: each of several large landmasses thought to have divided to form the present continents in the geologic past
    • the large landmasses were Gondwana, Pangaea, and Laurasia
  • lower species diversity
  • extinctions can occur when supercontinents are formed
    • different species on separate continents are forced to compete for food and habitats

Sea Level- Seafloor Spreading Rates

  • new oceanic crust is created at divergent boundaries
  • the amount of magma that rises and creates new crust at these boundaries changes over geologic time
  • more magma = rapid spreading, more mass and volume of new, hot and buoyant rock
    • elevation of seafloor is raised
    • volume of space in ocean basins to hold water is reduced
    • sea level rises

Example: Seafloor Spreading in the Cretaceous

  • 110-85 million years ago
  • much faster spreading, so there is a lot of new oceanic crust
  • global seas level> 660 feet higher than today
  • shallow seas covered continents like North America
  • the world climate was much warmer than it is today
  • the rate of extinction of land-animal species increased